Reaction mechanisms of fast neutrons on stable Mo isotopes below 21 MeV

Abstract

A large number of new measurements with the activation technique were performed for (n,2n) and neutron-induced Z = 1,2 reaction cross sections on the stable molybdenum isotopes in the energy range from 13.5 to 21 MeV. First results were obtained for the 92 Mo(n,2n) Mo(n,x) 97 Nb m , and 100 Mo(n,α) 97 Zr reactions, above 16 MeV. A significant number of high-accuracy 14 MeV measurements were performed which are in good agreement with the measurements above 16 MeV for reactions studied in both energy ranges. The rather complete database for the molybdenum isotopes was analyzed with two different sets of consistent model calculations: a local and a global approach. The global approach (a blind calculation with the TALYS code) provides a good overall description of the dominant reaction channels, although the (n,α) reactions for the heavy isotopes are overpredicted. The local approach (an adjusted calculation with the STAPRE-H code) describes the shapes and magnitudes of the excitation functions well from the reaction thresholds up to 21 MeV using a consistent parameter set, which was optimized based on all experimental information for the nuclei at hand and their immediate neighbors. The agreement between experimental and calculated data is, in general, good both at the maxima and at the tails of the excitation functions, and both for total activation cross sections of a particular channel and for cross sections leading to isomers, showing the viability of the level densities, the optical models, and the γ widths. Comparison of the two model calculations with the data indicates the relevance of an appropriate treatment for preequilibrium (PE) α-particle emission for the description of the data above 14 MeV. Comparison between the model calculations shows largely different PE deuteron emission contributions to the total ( Z = 1, A = 1) cross sections with an additional marked difference in energy dependence. This suggests that emission spectra around 20 MeV are required to establish the magnitude of the PE deuteron emission contribution to this process. New γ -ray strength functions were established by verification against average (n,γ ) data and were demonstrated to give good agreement with the measured isomer production cross sections.

Neutron activation cross sections on lead isotopes

“…In the case of 203 Pb m , the very short half-life required a fast pneumatic transport system to iterate between irradiation and counting. The methods employed here closely follow those of our earlier works [7][8][9][10][11][12][13]. Here, we concentrate on the features relevant for the present work.…”

Complementary optical-potential analysis of -particle elastic scattering and induced reactions at low energies

“…For the rest of statistical-model parameters we have used consistent sets established by analyzing various independent experimental data for all stable isotopes of V, Mn, Co, Ni, Cu [29,30,31], Mo [32], and Pd, Sn and Te [33], which finally allow us to focus on the uncertainties of the α-particle OMP. While a suitable description of the (α, n) reaction cross sections was found for lighter target nuclei with A≤54, a major overestimation of (α, γ) reaction cross sections resulted for 62,64 Ni, 63 Cu, 96,98 Ru, 106 Cd and 112,118 Sn.…”

“…They were carried out similarly to the previous analysis of (n, α) reaction cross section for A ∼90 [10,75], except the investigated OMP was now related to α-particles in the incident channel. For the rest of statistical-model parameters we have used consistent sets established by analyzing various independent experimental data for all stable isotopes of V, Mn, Co, Ni, Cu [29,30,31], Mo [32], and Pd, Sn and Te [33]. While a suitable description of the (α, n) reaction cross sections was found for lighter target nuclei with A≤54 (Fig.…”

“…4, starting with the accurate total-reaction cross sections of Vonach et al [28] and including the open questions recently noted for 63 Cu [20] and A ∼100 nuclei [14,15,21,22]. As a matter of fact, in order to calculate the reaction cross section we have used a consistent parameter set established by analyzing various independent exper-imental data for all stable isotopes of V, Mn, Co, Ni, Cu [29,30,31], Mo [32], Pd, Sn and Te [33]. Thus, it became possible to focus on the uncertainties of the α-particle OMP parameters and their improvement.…”

Fast-neutron induced pre-equilibrium reactions on 55Mn and 63,65Cu at energies up to 40 MeV

“…As part of a general investigation [1,2,3,4] of the reaction mechanisms of fast neutrons at low and medium energies, we have analyzed the activation cross sections of the odd-mass isotopes 55 Mn and 63,65 Cu in the excitation-energy range up to 50 MeV.…”